1. Field of the Invention
The present invention relates to photodiode arrays and epitaxial wafers, which use compound semiconductors, and manufacturing methods thereof. More particularly, the invention relates to photodiode arrays and epitaxial wafers, which use InGaAs/GaAsSb type-II semiconductors, and manufacturing methods thereof.
2. Description of the Background Arts
Recently, much research and development for group III-V compound semiconductors using an InP substrate has been promoted because the band gap energies of these compound semiconductors correspond to the near infrared region. Non-Patent Document 1 (R. Sidhu, “Long-wavelength Photodiode on InP Using Lattice-Matched GaInAs—GaAsSb Type-II Quantum Wells”, IEEE Photonics Technology Letters, The Institute of Electrical and Electronics Engineers, Volume 17, No. 12, pp. 2715-2717, (2005)) reports a photodiode having a cutoff wavelength of 2.39 μm, in which an absorption layer having an InGaAs—GaAsSb type-II multiple quantum well structure is formed on an InP substrate, and a pn junction is formed by a p-type or n-type epitaxial layer. Further, Non-Patent Document 1 proposes a photodiode having a cutoff wavelength of 2 μm to 5 μm, which uses an InGaAs—GaAsSb strain-compensated multiple quantum well structure in order to obtain such a longer cutoff wavelength.
Non-Patent Document 2 (M. Peter, “Light-emitting diodes and laser diodes based on a Ga1-xInxAs/GaAs1-ySby type II superlattice on InP substrate”, APPLIED PHYSICS LETTERS, American Institute of Physics, Volume 74, No. 14, pp. 1951-1953, (1999)) discloses light-emitting diodes (LEDs) each including an absorption layer having an InGaAs—GaAsSb type-II multiple quantum well structure, and an InP cladding layer grown on the absorption layer. The InP cladding layer in the LED is grown at 640° C., using phosphine (PH3) as a raw material for P.
Non-Patent Document 3 (D. Keiper, “Metalorganic vapour-phase epitaxy (MOVPE) growth of InP and InGaAs using tertiarybutylarsine (TBA) and tertiarybutylphosphine (TBP) in N2 ambient”, Journal of Crystal Growth, ELSEVIER, 204, pp. 256-262, (1999)) discloses growth of InGaAs and InGaAs/InP by metal-organic vapor phase epitaxy (MOVPE) using tertiarybutylarsine (TBAs), tertiarybutylphosphine (TBP), trimethylgallium (TMGa), and trimethylindium (TMIn), and investigation on growth condition dependence of surface defects during the growth. In Non-Patent Document 3, an epitaxial wafer having a low density of surface defects is obtained at a relatively high growth temperature of 660° C. or more.
Patent Document 1 (Japanese Laid-Open Patent Publication No. 2001-144278) discloses a photodiode array having a mesa structure in which photodiodes each composed of laminated semiconductor layers are isolated from each other by etching. This photodiode array is manufactured as follows. An n-type InP layer, an undoped InGaAs light absorption layer, and a p-type InP window layer are disposed in this order on an n-type InP substrate. The InGaAs light absorption layer and the p-type InP window layer are subjected to etching to form individual photodiodes isolated from each other, and the photodiodes are coated with an insulating film. Then, a p-type ohmic electrode is formed on the p-type InP window layer of each photodiode while a common n-type ohmic electrode is formed on the rear surface of the n-type InP substrate.